Electrical pick-up



Jan. 23, 1934. s. A. SOLLIE ELECTRICAL PICK-UP Filed Nov 19, 1931 2 SheetsSheet l INVENTQR SIGURD A. SOLLIE BY ATTORNEY Jan. 23, 1934. A SOLLIE 1,944,583

ELECTRICAL PICK-UP Filed Nov. 19, 1951 2 Sheets-Sheet 2 INVENTOR SIGURD A. SOLLlE ATTORNEY Patented Jan. 23, 1934 UNITED STATES PATENT OFFICE ELECTRICAL PICK-UP Application November 19, 1931, Serial No. 576,057, and in Great Britain November 24, 1930 Claims.

' chanical devices such as electric generators, telephone loud speakers and voice pick-ups, but it has to do more specifically with electric phonograph pick-ups.

Assuming it to be desired, as in the present case, to produce a phonograph pick-up of high quality and one which can, in addition, be manufactured commercially and maintained continuously in good working order, there are several major considerations to which the designer should give attention. The first is fidelity of response, by which is meant that the vibratory currents generated should be in true conformity to theundulations of the record groove. To approach a satisfactory degree of perfection in this respect it is necessary that the pick-up device be capable. of following the record undulations accurately and not have any substantial tendency to ride the groove or choose its own course. The determinant factors in this respect are the stiffness of the armature and the pressure on the stylus. By the term stiffness is meant the resistance which the armature assembly presents against actuation in response to the record undulations. A certain amount of stiffness as thus defined is inherently unavoidable in any pick-up of the electromagnetic type because of the necessity of centering the armature with respect to the field poles. The greater the stiffness, however, (other things being equallthe greater is the departure from true fidelity of reproduction.

Stiffness can be offset, in a measure at least, by increasing the pressure of the stylus on the record. But increased pressure spells increased record wear, and this is another major consideration in phonograph pick-up design. Record wear increases rapidly with increased stylus pressure. The phonograph pick-up should, therefore, be designed for the lowest possible pressure consistent with the desired quality of reproduction. It follows that one of the first objectives in pick-up design is to restrict the stiffness of the armature assembly as much as possible, since this determines the necessary stylus pressure.

Another factor which is apt to cause distorted reproduction, if not carefully guarded against, is the natural resonant period of the armature and other parts of the pick-up. If any of the parts or combination of parts has a natural period within the range of frequencies which it, is de I sired to reproduce, and the natural vibration. of such parts is capable of being reflected intothe magnetic circuit, it is manifest that distortion will occur in the reproduction, offrequencies. at and near the natural periods of such parts. must, therefore, be exercised to avoid the intru-v sion of interferingnatural vibrations.

Objectionable resonant vibrations are. mos likely to occur in the armature assembly, which consists generally of the armature. and its supports, together with the medium through which the stylus is connected with the armature. If these parts are of rugged design their natural vibrations are not likely to be sufiiciently pronounced to cause any objectionable distortion. But, on the other hand, sufficient ruggedness of structure may, under certain conditions, result in high mechanical inertia, which is a form;v of stiffness and, accordingly, undesirable.

Another factor that should not be overlooked is that of maintenance. Rubber is the most satisfactory material to use as av resilient damp.- ing agency in phonograph pick-ups, but rubber deteriorates and loses its resiliency. Consequently, it must be replaced from time totime if the pick-up is to be kept. in good operating condition. It is, thus, highly desirable that the pick-up design be such that the rubber damper may be easily renewed, preferably withoutdiS: assembling or disturbing any adjustment of the pick-up.

The principal object of this invention is to devise a phonograph pick-up capable of functioning with the utmost fidelity and with a minimum of wear on the records.

Another object is to devise a pick-up which can be easily maintained in good order continuously. Still another object is to devise a pick-up which, while embodying to a high degree all the desired operating characteristics, is well adapted to commercial production and is not likely to require time consuming delicate adjustments during or after assembly.

Pursuant to the ultimate objects just stated, there are certain contributory objects which this invention seeks to achieve. The first is to devise a pick-up having a minimum of stiffness, which term includes all factors tending to restrain the free movementof the armature and stylus in conformity to the record undulations. The second contributory object is to achieve lightness of stylus pressure on the record, which, as previously explained, is largely, if not wholly, dependent upon the stifiness factor. The third contributory Care object is to design the pick-up so that there will be no pronounced resonant vibrations developed in the armature assembly or other parts as a result of which corresponding distortions might occur. The fourth contributory object is to design the pick-up so that the rubber damper may be easily removed from time to time for replacement without having to dis-assemble the device or in any way impair its operation.

Tests of my invention have shown that by its use the frequency range may be increased to cover a range from 30 cycles to 8,000 cycles, and the curves obtained show a remarkable absence of the major resonancescommon to pick-up units. These test pick-ups embodying my invention were made from ordinary commercial materials. With higher permeability steels even better results can probably be obtained.

Although this invention is directed primarily to a phonograph pick-up device, the underlying principles and characteristic features are also applicable in whole or in part to other related devices, such as telephone loud speakers, voice pick-ups, and electric generators for certain special uses (other than phonograph pick-ups). As an example, one of the phonograph pick-ups herein described has been adapted to operate a driving unit for a loud speaker connected to a radio receiver. On the other hand, the problems involved in the design of a phonograph pick-up are not by anymeans the same as those met with in loud speaker design or ordinary electric generator design.

In the drawings,

Fig. 1 is a cr0ss-section of the device of my in-- vention;

Fig. 2 is a cross-section Fig. 1;

Fig. 3 is a schematic showing how the device is applied to a phonograph record;

Fig. 4 is an elevation of my device; and

Fig. 5 is an exploded view showing the parts composing my device, and the manner of its assembly.

Like numbers refer to the same parts in all the figures. a

The unit as shown has a polarizing permanent magnet 1 with two U-shaped pole pieces 12 arranged between its limbs. Clamped between one of the pairs of opposing faces of the pole pieces is a third or central pole piece 3 extending toward the other pair of pole faces. The pole pieces are clamped in position by means of a non-magnetic bolt 4 and for the purpose of interrupting the magnetic ilux path through the members non-magnetic spacers 5 are interposed between the U-shaped pieces and the central pole piece. These spacers 5 are of a thickness calculated to provide a magnetic reluctance or" along line 2 -2 of the same order as the air gaps 6 between the other pair of faces of the Llhaped pole pieces and the armature Z pivoted adjacent them.

' The central pole piece% is surrounded by a bobbin 8 carrying an inductivecoil 9 susceptible to changes in flux in the central pole piece.

The armature 7, which is. spear-headed in shape, is pivotally supported in a nonmagnetic bracket 10 on a spindle 11 passing through a The bracket 10 has up drilling in the armature. wardly extending flanges 13 which embrace the pole pieces 12, and is secured thereto by studs 14. The flanges thus provide bearings for the axle 11.

The bracket 19 is provided with a boss 15 apertured for the passage, therethrough of the armature shankl'? and a sleeving of soft rubber 16 surrounding this shank. The shank has an aperture 18 of diamond shape for reception of a phonograph needle.

In order to maintain the needle in rigid contact.

with the armature there is provided a spring clip 19 having a pair of arms, embracing the armature shank, and a depending spring limb, the foot 20 of which is turned inwards to cover a portion of the needle aperture. The spring clip may be rigidly attached to the armature shank, for example, by soldering or other means, and forms by the spring action of its foot 20 co-operating with the diamond shaped'aperture 18 an effective nee dle clamp.

Preferably the Lleshaped pole pieces 12 and the third orcentral pole piece 3, together with the "rmature '7, are made from a high permeability material such as silicon iron, and in order to preclude the possibility of magnetic short-circuiting, the bolt l and the bracket 10 are made from now-magnetic material such as brass.

It will be observed that the pair of limbs of the pole pieces 12 embracing the armature are cut away angularly for cooperation with the spearshaped head thereof to form the air gaps 6. The armature is pivoted in stable equilibrium between these pole pieces, and in its non-playing stable position is centrally disposed between the pole pieces so that the air gaps on either side are of equal size and thus of equal magnetic reluctance. The arrangement therefore forms a balanced Wheatstone bridge circuit with respect to magnetic fluxes through the third or central pole piece 3. In other Words, the flux provided by the polarizing magnet 1 passes from one limb thereof to the other along the two parallel paths formed by the upper and lower limbs of the U-shaped pole pieces 12, and with the armature in its central position no fiux threads the central pole piece 3. It is to be noted, as a feature of my invention, that flux from the permanent magnet threads the armature through one path only and not throughtwo paths as is usual in pick-ups hitherto known.

When the armature is displaced from its central position, due to a needle secured in the aperture 18 following the groove of a phonograph record, the magnetic balance of the arrangement is disturbed by the increase of oneof the air gaps 6 and the corresponding decrease of the other due the armature result in a continual reversal of direction and change of quantity of flux threading the third pole piece 3, and electromotive forces proportionately varying in direction and quantity are generated thereby in the inductive winding 9, from which they are tapped in known manner.

moving system of the pick-up described has low inertia and low restraining force, so that small efiort is required for displacement. It follows that only a very low pressure is necessary to hold the needle point in the groove of the record. In

fact experience has shown that this pressure is as low as 1.8 ounces. Consequently, the life of a record is increased many times.

No adjustments are required to ensure the arits iio

its

mature being in correct location with respect to the pole pieces. The quality of manufacture controls the various clearances so that, if the pieces are made correctly, a uniform product is assured.

What is claimed is:

1. A phonograph pick-up comprising a magnet, a pair of opposed pole pieces of opposite polarity for said magnet, each pole piece having two faces and the faces of one being opposed to the faces of the other, a magnetic flux conductor interposed between said opposed pole pieces and insulated therefrom and clamped between one pair of opposed faces, an electrical conductor surrounding said flux conductor, and an armature pivoted between said other pair of opposed faces and symmetrically spaced with respect thereto and the other end of said flux conductor.

2. An electromagnetic pick-up comprising a magnet, a two faced pole piece secured to one pole of said magnet, a second two-faced pole piece secured to the other pole of said magnet opposite said first pole piece, a neutral pole piece secured at one end between two opposing faces of said pole pieces and spaced therefrom by nonmagnetic spacers and having its free end positioned adjacent the other two opposing faces of said pole pieces, an electrical conductor surrounding said neutral pole, a pivoted armature equally spaced between the other two faces, with its pivot therebetween, and symmetrically disposed with respect to the free end of said neutral pole piece.

3. In an electromagnetic device operable to convert oscillatory mechanical energy into corresponding oscillatory electrical energy and vice versa, a pivotally supported armature, a magnetic field structure comprising a north pole piece having two legs, a south pole piece having two legs in opposed relation to the respective legs of the north pole pieces, and a neutral pole piece secured at one end to one pair of opposed legs and having its other end free and disposed in proximity to said other pair of legs, said armature and its pivotal axis being disposed directly between said north and south pole pieces in the space between the opposed legs and juxtaposed free end of the neutral pole piece, there being an air gap between said armature and each of said north and south pole pieces, said neutral pole piece being closely adjacent said armature and forming therewith a magnetic air gap of substantially constant reluctance, said armature ductor having one end interposed between and insulated from one pair of opposed pole faces and having its other end terminating in proximity to the other pair of opposed pole faces, an electrical conductor surrounding said flux conductor, and an armature symmetrically spaced with respect to said other pair of opposed pole faces and the juxtaposed end of the flux conductor and pivoted to move about an axis lying between and parallel to the said other pair of opposed faces.

5. A phonograph pick-up comprising a magnet, a pair of opposed pole pieces of opposite polarity for said magnet, each pole piece having two faces with the faces of one positioned opposite the faces of the other, a magnetic fiux conductor having one end interposed between and insulated from one pair of opposed. pole faces and having its other end terminating in proximity to the other pair of opposed pole faces, an electrical conductor surrounding said flux conductor, a non-magnetic bracket carried by said pole pieces, and an armature supported by said bracket in symmetrical spaced relation to said other pair of opposed faces and the juxtaposed end of the flux conductor and pivoted. upon said magnetic bracket to move about an axis lyingbetween and parallel to the said other pair of opposedfaces.

SIGURD A. SOLLIE. 

